Brian McCall

The orthocenter is the point of concurrency of the altitudes in a triangle. A point of concurrency is the intersection of 3 or more lines, rays, segments or planes. The orthocenter is just one point of concurrency in a triangle. The others are the incenter, the circumcenter and the centroid.

One of the four main points of concurrencyof a triangle is the orthocenter.The orthocenter is where thethree altitudes intersect.

If we look at three different types of triangles,if I look at an acute triangleand I drew in one of the altitudes orif I dropped an altitude as somemight say, if I drew in another altitude,then this point right here willbe the orthocenter.I could also draw in the third altitude,but I know that since this is a pointof concurrency the three altitudes mustintersect there so I only haveto draw two.

If we look at a right triangle, if I wereto draw in an altitude from that vertex,well, that just happens to be thisleg of this right triangle.If I drew in the altitude of this triangle,then I would see -- excuse me, thisside, then this leg wouldbe its altitude.And if we drew in this last one from our90-degree angle, we see that the pointwhere they are concurrent is rightat the vertex of that right angle.So in a right triangle your orthocenterwill be at the vertex of the rightangle.

And, last, if we look another an obtusetriangle, we remember in order to findthe altitude of this side we have to extendthat side drop down an altitudewhich is outside of our triangle to find-- and I'm just going to extendthis -- to find the ortho -- to findthe altitude from this vertex, I'mgoing to draw a perpendicularsegment through the vertex.So it looks like it's going to intersectright over there, and for this thirdside I would have to extend it untilwe could find our 90-degree angle.Okay.

So in an obtuse triangle your orthocenterwill be outside of your triangle.So expect that on a quiz.